1. Field of the Invention
The present invention relates generally to the field of image reproduction, and more particularly to systems and methods for reducing the appearance of noise in the reproduction of images.
2. Background of the Invention
When reproducing images, it is generally preferred to have the colors in the reproduced image match the colors in the original source. The colors in the reproduction are typically rendered using a mixture of primary tones.
Problems occur, however, when trying to match user expectations on pure/primary tone reproductions in, for example, a copier. Due to mismatch in color gamut between the input device, such as from a scanner, and the image displaying device, such as a printer, what may be perceived as a primary tone (e.g., red, green, blue, cyan, magenta, yellow, black, and white) in the original image, may be rendered using a combination of tones in the outputted image. While printer color tables may be designed to output minimal primaries with low halftone noise for a given color input, this property may not be preserved in a copier due to scanner and printer gamut mismatch. Even if the color being reproduced is within the color gamut of the displaying device, halftoning artifacts, arising as a result of mixing a small amount of some primary tone with other tones, may result in an appearance that is objectionable even though the average color is correctly reproduced. Furthermore, the presence of other artifacts, such as scanning noise, may also add to this problem. Thus, while from a colorimetric point of view, a correct tone, as compared to the original image, may have been reproduced, the presence of multiple, half toned colors in the output tone may be considered less acceptable by a user.
To improve the perceived quality of a reproduced image, a number of noise reduction techniques have been developed. Many of these techniques focus on reducing scanner noise; however, such noise reduction techniques do not guarantee pure tone reproduction. Thus, while a pure tone may be smoothed to eliminate pixel noise, it may map to a tone that is rendered with multiple tones.
A number of tone separation techniques have also been presented to attempt to minimize the use of primaries for the reproduction of an image, for example by a printer. However, different input image data or devices, for example from different scanners or scans, provide different inputs to the display device resulting in multiple tones at the output.
Further methods to improve the perceived quality of a reproduced image have involved improving dither noise. However, such efforts have focused on reducing dither noise and typically have not addressed the issue of pure-tone rendering.
Accordingly, systems and methods are needed that provide noise reduction for primary tones for image replication systems.